On the feasibility of using a laser guide star adaptive optics system in the daytime

Abstract. We investigate the use of ultra-narrow band interference filters to enable daytime use of sodium laser guide star (LGS) adaptive optics systems. Filter performance is explored using theoretical and vendor supplied filter transmission profiles, a modeled daylight sky background, broadband measurements of the daytime sky brightness on Maunakea, and an assumed photon return from the sodium LGS and read noise for the wavefront sensor (WFS) detector. The critical parameters are the bandpass of the filter, the out-of-band rejection, and the peak throughput at the wavelength of the LGS light. Importantly, a systematic trade between these parameters leads to potentially simple solutions enabling daytime observations. Finally, we simulated the Mid-Infrared Adaptive Optics (MIRAO) system planned for the Thirty Meter Telescope with an end-to-end simulation, folding in daytime sky counts. We find that MIRAO with five sodium LGSs, commercial off-the-shelf filters to suppress the sky background in the LGS WFSs, and a near-infrared natural guide star (K  ≤  13) tip/tilt/focus WFS can attain daytime Strehl ratio values comparable to those at night.